Friction block



Patented Feb. 16, 1937' FRICTION BLOCK George W. Nickerson, Butte, Mont.

No Drawing. Application August 9, 1935, Serial 3 Claims.

This invention relates to a friction block adapted to serve, for example, as an article of desk furniture, affording a convenient source of friction powder to which one may resort whose occupa- 5 tion involves the manipulation of sheets having small inertia as in counting paper money, playing cards, turning leaves, etc., for rubbing his finger against the block, thereby transferring to the surface of the finger enough of the friction enhancing agent to improve the frictional hold of the finger upon the sheets.

One of the objects of the invention is to provide a friction block including a matrix substance having an extremely low coefficient of attrition under the rubbing action of the finger and holding in pulverulent form a friction enhancing substance such as powdered rosin.

Another object of the invention is to provide a friction block the substance of which is capable of being transferred to the finger in minute quantity as a friction powder and which is not of asticky or tacky nature, harmless to the human skin and leaving no mark or stain upon the fingers and as little as possible of its friction producing effect upon the papers, book pages or objects touched.

Specifically, the object of the invention is to produce a composition of matter for the purpose specified comprising finely comminuted rosin set up in a matrix of plaster of Paris, the proportions of the ingredients being selected to produce to an optimum degree the desirable qualities of a friction powder as before above set forth.

Other objects of the invention will appear as the following description of a preferred. and practical embodiment thereof proceeds.

Since the invention does not concern itself with the structure or shape of the embodiment in which the friction block is provided, but only in the nature of a composition of matter by which it is constituted, the disclosure is believed to be complete without a drawing.

In casting about for the choice of a substance capable of enhancing the tactile friction of the fingers. rosin was naturally selected, but in its lump form it was found to be too solid to come away on the finger in suflicient quantity to be noticeably effective, while in its powdered form, it was not only readily spilled, but tended in time and particularly in damp weather to coalesce.

The problem of the present invention was therefore to find a matrix substance which would hold the granules of powdered rosin with just the correct bond to permit it to come away on the finger together with the matrix substance in just the right quantity to effect its purpose in preventing relative slippage between the finger and sheets whileat the same time being free from stickiness or tackiness.

The invention as finally evolved comprises pow- 5 dered rosin held in a matrix of plaster of Paris. In preparing the friction enhancing composition I have found that the average proportions for the best results are roughly three parts of powdered rosin to two parts of plaster of Paris 10 by weight with a sufiicient quantity of water added to produce a semi-liquid paste after which the product should be allowed to set. An excess of water is undesirable since it may cause a fiotation separation of the rosin from the plaster 15 of Paris.

The above proportions are not critical; increasing the rosin content of the substance results in a softer, more friable product, having an effect more closely approaching that of powdered rosin. 20 Increasing the plaster of Paris content results in a harder product, less easily abraded, being less tacky, but with inferior power to prevent slippage between the finger and paper. When the block has set and the moisture has evaporated to dry- 25 ness the block is ready for use. In counting money, it is necessary merely at intervals to. rub the finger lightly against the block whereupon the desired frictional quality will have been imparted to the finger without creating a feeling of 30 stickiness and without any appreciable amount of the substance being transferred to the paper or material which is touched.

Since there are numerous kinds of rosin, difficulty may sometimes be experienced in making 35 a product of the right consistency. The product may appear too tacky when the proportion of rosin is increased and too hard to be abraded when the proportion of plaster of Paris is increased to the point at which the tackiness of the 40 mass is sufiiciently reduced. This difiiculty can usually be overcome by adding a sufiiicient quantity of some filler, preferably of a white color and which reduces the tacky effect of the rosin as well as softening the matrix substance. I have found that talc, infusorial earth, powdered chalk, or other similar substances are well suited to the purpose.

While it is within the purview of the invention to employ other matrix substances than plaster 50 a of Paris, I have found that the peculiar manner in which plaster of Paris crystallizes assures the homogeneity of two substances whose weights are so related that one will sink while the other fioats in water. When plaster of Paris which is hemi- 55 hydrate of calcium is mixed with water, the latter dissolves some of the hemihydrate which unites with water to form dihydrate of calcium. Since the latter is less soluble than the former it crystallizes from the solution and more of a hemihydrate dissolves the process continuing until the plaster of Paris has been changed into a mass of interlocking crystals from which the excess of water finally evaporates. The progressiveness of the crystal formation seems to assure the interlocking of the particles of rosin between the elements of the crystalline structure instead of them being pushed out of the crystal mass into whatever excess of water may be present as would be the case with substances which crystallize along other patterns.

While I have in the above description disclosed what I believe to be a preferred and practical form of the invention, it will be understood by those skilled in the art that the specific substances and proportions as described are merely by way of example and not to be construed as limiting the scope of the invention as claimed.

What I claim is:

1. Composition of matter block which in the abraded form has the property of enhancing friction comprising rosin in pulverulent form set in a matrix of plaster of Paris, the proportions by weight being approximately three parts of rosin and two parts of plaster of Paris.

2. Composition of matter block, in the abraded form having the property of enhancing friction comprising rosin in pulverulent form set in a matrix of plaster of Paris mixed with a filler, the proportions by weight of rosin and plaster of Paris being approximately three parts of the former and two parts of the latter.

3. Composition of matter block which in the abraded form has the property of enhancing friction comprising rosin in pulverulent form homogeneously distributed through and held in a solid matrix of plaster of Paris.

GEORGE W. NICKERSON. 

